Virtual retinal display with eye tracking

ABSTRACT

Light emitted from a virtual retinal display light source passes through a beamsplitter to a scanning subsystem and on to an eyepiece and the viewer&#39;s eye. Some of the light is reflected from the viewer&#39;s eye passing back along the same path. Such light however is deflected at the beamsplitter toward a photodetector. The reflected light is detected and correlated to the display scanner&#39;s position. The content of the reflected light and the scanner position for such sample is used to generate a map of the viewer&#39;s retina. Such map includes `landmarks` such as the viewer&#39;s optic nerve, fovea, and blood vessels. The map of the viewer&#39;s retina is stored and used for purposes of viewer identification. The viewer&#39;s fovea position is monitored to track where the viewer is looking.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation in part of U.S. patent application Ser. No.09/008,918 filed Jan. 20, 1998, now U.S. Pat. No. 5,982,555, for VirtualRetinal Display with Eye Tracking. The content of that application isincorporated herein by reference and made a part hereof.

BACKGROUND OF THE INVENTION

This invention relates to retinal display devices, and more particularlyto a method and apparatus for mapping and tracking a viewer's eye.

A retinal display device is an optical device for generating an imageupon the retina of an eye. Light is emitted from a light source,collimated through a lens, then passed through a scanning device. Thescanning device defines a scanning pattern for the light. The scannedlight converges to focus points on an intermediate image plane. As thescanning occurs the focus point moves along the image plane (e.g., in araster scanning pattern). The light then diverges beyond the plane. Aneyepiece is positioned along the light path beyond the intermediateimage plane at some desired focal length. An "exit pupil" occurs shortlybeyond the eyepiece in an area where a viewer's eye pupil is to bepositioned.

A viewer looks into the eyepiece to view an image. The eyepiece receiveslight that is being deflected along a raster pattern. Modulation of thelight during the scanning cycle determines the content of the image. Fora see-through virtual retinal display a user sees the real worldenvironment around the user, plus the added image of the displayprojected onto the retina.

SUMMARY OF THE INVENTION

A viewer wearing a head-mounted virtual retinal display typically movestheir eye as they look at images being displayed. According to theinvention, the direction the viewer looks is tracked with the display.Prior to tracking, a map of the viewer's eye is generated by thedisplay. The map includes `landmarks` such as the viewer's optic nerve,fovea, and blood vessels. Thereafter, the relative position of one ormore landmarks is used to track the viewing direction. The head-mounteddisplay includes a light source and a scanner. The scanner deflectslight received from the light source to scan a virtual image onto aviewer's retina in a periodic manner. During each scanning period, lightis deflected along a prescribed pattern. To generate a map, andthereafter to monitor viewing direction, light reflected off theviewer's retina is monitored. Some of the reflected light travels backinto the display device. The content of the reflected light will varydepending upon the image light projected and the features of theviewer's retina. During the initial mapping stage, the content of theimage light can be fixed at a constant intensity, so that the content ofthe reflected light is related only to the feature's (i.e., landmarks)of the retina. The changing content of the reflected light is sampled ata sampling rate and stored. The scanner position at the time of eachsample is used to correlate a position of the sample. The relativeposition and the content represent a map of the viewer's retina.

According to one aspect of the invention, the light reflected from theviewer's eye travels back into an eyepiece and along a light path withinthe retinal display device. In a specific embodiment the reflected lightis deflected by the scanner toward a beamsplitter. The beamsplitterdeflects the reflected light toward a photodetector which samples thereflected light content. The beamsplitter is positioned between thelight source and the scanner of the retinal display device.

For generating a virtual image, light emitted from the light sourcepasses through the beamsplitter to the scanning subsystem and onward tothe eyepiece and the viewer's eye. Light reflected from the viewer's eyepasses back along the same path but is deflected so as not to return tothe light source. Instead the light is deflected toward thephotodetector. Thus, the beamsplitter passes light which is incident inone direction (e.g., light from the light source) and deflects lightwhich is incident in the opposite direction (e.g., reflected light fromthe viewer's eye).

According to another aspect of the invention, a specific feature of theretina (e.g., fovea position) is monitored over time to track where theviewer is looking (i.e., the viewer's center of vision). The landmarksin the retina which correspond to such feature will cause the reflectedlight to exhibit an expected pattern. The relative position of suchpattern in the reflected light will vary according to the viewingdirection. By identifying the pattern and correlating the relativeorientation of the pattern to the orientation of the correspondingfeature in the map, the change in viewing direction is determined. Invarious applications, such position indication is used as a pointingdevice or is used to determine image content. For example, as a pointingdevice the fovea position indicates pointer position. A blink of the eyefor example, corresponds to actuating a pointing device (e.g.,"clicking" a computer mouse.)

According to another aspect of the invention, the map of the viewer'sretina is stored and used for purposes of viewer identification. In asecurity application for example, a viewer is denied access toinformation or denied operation of a computer or display when theviewer's retina does not correlate to a previously stored map of anauthorized user.

According to an advantage of the invention, the display can track wherea viewer is looking, use the viewer's eye as a pointer, and identify theperson using the display. These and other aspects and advantages of theinvention will be better understood by reference to the followingdetailed description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an optical schematic diagram of a virtual retinal displayhaving an eye tracking capability according to an embodiment of thisinvention;

FIG. 2 is a perspective drawing of an exemplary scanning subsystem forthe display of FIG. 1;

FIG. 3 is a diagram of a viewer's retina mapped according to anembodiment of this invention;

FIG. 4 is a diagram of the viewer's retina of FIG. 3 at a time when theviewer looks in a different direction;

FIG. 5 is a diagram of a display image;

FIG. 6 is a diagram of a display image after a viewer clicks on a buttonon the display imagery; and

FIG. 7 is a diagram of a display image after a viewer clicks on a targetamong the display imagery.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Overview

FIG. 1 is an optical schematic diagram of a virtual retinal display 10according to an embodiment of this invention. The retinal display 10generates and manipulates light to create color or monochrome imageshaving narrow to panoramic fields of view and low to high resolutions.Light modulated with video information is scanned directly onto theretina of a viewer's eye E to produce the perception of an erect image.The retinal display is small in size and suitable for hand-heldoperation or for mounting on the viewer's head. The display 10 includesan image data interface 11 which receives image data in the form of avideo or other image signal, such as an RGB signal, NTSC signal, VGAsignal or other formatted color or monochrome video or image datasignal. The image data is generated by a processor 13 or other digitalor analog image data source. The image data interface 11 generatessignals for controlling a light source 12 and for synchronizing thescanner subsystem 16. Light generated by the display 10 is alteredaccording to the image data to generate image elements (e.g., imagepixels) which form an image scanned onto the retina of a viewer's eye E.The light source 12 includes one or more point sources of light. In oneembodiment red, green, and blue light sources are included. In oneembodiment the light source 12 is directly modulated. That is, the lightsource 12 emits light with an intensity corresponding to a drive signal.In another embodiment the light source 12 outputs light with asubstantially constant intensity that is modulated by a separatemodulator in response to the drive signal. The light output along anoptical path thus is modulated according to image data within the imagesignal. Such modulation defines image elements or image pixels.Preferably the emitted light is spatially coherent.

The retinal display 10 also includes a scanning subsystem 16, aneyepiece 20 and an eye mapper 40. The light 36 emitted from the lightsource 12 and passing through the optics subsystem 14 is deflected bythe scanner subsystem 16 toward the eyepiece 20 and the viewer's eye E.In one embodiment the scanning subsystem 16 receives a horizontaldeflection signal and a vertical deflection signal (e.g., SYNCH signals)derived from the image data interface 11. Typically the light isdeflected along a prescribed pattern, such as a raster pattern, althoughin an alternative embodiment another display format such as vectorimaging can be used. In one embodiment, the horizontal scanner includesa mechanical resonator for deflecting passing light, such as thatdescribed in U.S. Pat. No. 5,557,444 to Charles D. Melville entitled,"Miniature Optical Scanner for a Two Axis Scanning System," which isincorporated herein by reference. Alternatively, the horizontal scannermay be an acousto-optic device or a resonant or non-resonantmicro-electromechanical device. The scanning subsystem includes ahorizontal scanner and a vertical scanner. The eye mapper 40 monitorsthe position of the viewer's eye based upon light reflected back intothe display from the viewer's eye.

Light Source

The light source 12 includes a single or multiple light emitters. Forgenerating a monochrome image a single monochrome emitter typically isused. For color imaging, multiple light emitters are used. Exemplarylight emitters include colored lasers, laser diodes or light emittingdiodes (LEDs). Although LEDs typically do not output coherent light,lenses are used in one embodiment to shrink the apparent size of the LEDlight source and achieve flatter wave fronts. In a preferred LEDembodiment a single mode monofilament optical fiber receives the LEDoutput to define a point source which outputs light approximatingcoherent light.

Where the light emitters are externally modulated, the display device 10also includes a modulator responsive to an image data signal receivedfrom the image data interface 11. The modulator modulates the visiblelight emitted by the light emitters to define image content for thevirtual imagery scanned on a viewer's eye E. The modulator is anacoustooptic, electrooptic, or micro-electromechanical modulator.

Additional detail on these and other light source 12 embodiments arefound in U.S. patent application Ser. No. 08/437,818 for "VirtualRetinal Display with Fiber Optic Point Source" filed May 9, 1995, andincorporated herein by reference.

According to alternative embodiments, the light sources or the lightgenerated by the point sources are modulated to include red, green,and/or blue components at a given point (e.g., pixel) of a resultingimage. Respective beams of the point sources are modulated to introducecolor components at a given pixel.

Image Data Interface

The retinal display device 10 is an output device which receives imagedata to be displayed. Such image data is received as an image datasignal at the image data interface 11. In various embodiments, the imagedata signal is a video or other image signal, such as an RGB signal,NTSC signal, VGA signal or other formatted color or monochrome video orgraphics signal. An exemplary embodiment of the image data interface 11extracts color component signals and synchronization `SYNCH` signalsfrom the received image data signal. In an embodiment in which an imagedata signal has embedded red, green and blue components, the red signalis extracted and routed to a modulator for modulating a red light pointsource output. Similarly, the green signal is extracted and routed to amodulator for modulating the green light point source output. Also, theblue signal is extracted and routed to a modulator for modulating theblue light point source output.

The image data signal interface 11 extracts a horizontal synchronizationcomponent and vertical synchronization component from the image datasignal. In one embodiment, such signals define respective frequenciesfor horizontal scanner and vertical scanner drive signals routed to thescanning subsystem 16.

Scanning Subsystem

The scanning subsystem 16 is located after the light source 12, eitherbefore or after the optics subsystem 14. In one embodiment the scanningsubsystem 16 includes a resonant scanner 200 for performing horizontalbeam deflection and a galvanometer for performing vertical beamdeflection. The scanner 200 serving as the horizontal scanner receives adrive signal having a frequency defined by the horizontalsynchronization signal extracted at the image data interface 11.Similarly, the galvanometer serving as the vertical scanner receives adrive signal having a frequency defined by the vertical synchronizationsignal VSYNC extracted at the image data interface. Preferably, thehorizontal scanner 200 has a resonant frequency corresponding to thehorizontal scanning frequency.

Referring to FIG. 3 the scanner 200 includes a mirror 212 driven by amagnetic circuit so as to oscillate at a high frequency about an axis ofrotation 214. In one embodiment the only moving parts are the mirror 212and a spring plate 216. The optical scanner 200 also includes a baseplate 217 and a pair of electromagnetic coils 222, 224 with a pair ofstator posts 218, 220. Stator coils 222 and 224 are wound in oppositedirections about the respective stator posts 218 and 220. The electricalcoil windings 222 and 224 may be connected in series or in parallel to adrive circuit as discussed below. Mounted on opposite ends of the baseplate 217 are first and second magnets 226, the magnets 226 beingequidistant from the stators 218 and 220. The base 217 is formed with aback stop 232 extending up from each end to form respective seats forthe magnets 226.

The spring plate 216 is formed of spring steel and is a torsional typeof spring having a spring constant determined by its length and width.Respective ends of the spring plate 216 rest on a pole of the respectivemagnets 226. The magnets 226 are oriented such that they have like polesadjacent the spring plate.

The mirror 212 is mounted directly over the stator posts 218 and 220such that the axis of rotation 214 of the mirror is equidistant from thestator posts 218 and 220. The mirror 212 is mounted on or coated on aportion of the spring plate.

Magnetic circuits are formed in the optical scanner 200 so as tooscillate the mirror 212 about the axis of rotation 214 in response toan alternating drive signal. One magnetic circuit extends from the toppole of the magnets 226 to the spring plate end 242, through the springplate 216, across a gap to the stator 218 and through the base 217 backto the magnet 226 through its bottom pole. Another magnetic circuitextends from the top pole of the other magnet 226 to the other springplate end, through the spring plate 216, across a gap to the stator 218and through the base 217 back to the magnet 226 through its bottom pole.Similarly, magnet circuits are set up through the stator 220.

When a periodic drive signal such as a square wave is applied to theoppositely wound coils 222 and 224, magnetic fields are created whichcause the mirror 212 to oscillate back and forth about the axis ofrotation 214. More particularly, when the square wave is high forexample, the magnetic field set up by the magnetic circuits through thestator 218 and magnets 226 and 228 cause an end of the mirror to beattracted to the stator 218. At the same time, the magnetic fieldcreated by the magnetic circuits extending through the stator 220 andthe magnets 226 cause the opposite end of the mirror 212 to be repulsedby the stator 220. Thus, the mirror is caused to rotate about the axisof rotation 214 in one direction. When the square wave goes low, themagnetic field created by the stator 218 repulses the end of the springplate 216 whereas the stator 220 attracts the other end of the springplate 216 so as to cause the mirror 212 to rotate about the axis 214 inthe opposite direction.

In alternative embodiments, the scanning subsystem 14 instead includesacousto-optical deflectors, electro-optical deflectors, rotatingpolygons or galvanometers to perform the horizontal and vertical lightdeflection. In some embodiments, two of the same type of scanning deviceare used. In other embodiments different types of scanning devices areused for the horizontal scanner and the vertical scanner.

Optics Subsystem

The optics subsystem 14 receives the light output from the light source,either directly or after passing through the scanning subsystem 16. Insome embodiments the optical subsystem collimates the light. In anotherembodiment the optics subsystem converges the light. Left undisturbedthe light converges to a focal point then diverges beyond such point. Asthe converging light is deflected, however, the focal point isdeflected. The pattern of deflection defines a pattern of focal points.Such pattern is referred to as an intermediate image plane.

Eyepiece

The eyepiece 20 typically is a multi-element lens or lens systemreceiving the light beam(s) prior to entering the eye E. In analternative embodiment the eyepiece 20 is a single lens. The eyepiece 20serves to relay the rays from the light beam(s) toward a viewer's eye.In particular the eyepiece 20 contributes to the location where an exitpupil of the retinal display 10 forms. The eyepiece 20 defines an exitpupil at a known distance from the eyepiece 20. Such location is theexpected location for a viewer's eye E.

In one embodiment the eyepiece 20 is an occluding element which does nottransmit light from outside the display device 10. In an alternativeembodiment, an eyepiece lens system 20 is transmissive so as to allow aviewer to view the real world in addition to the virtual image. In yetanother embodiment the eyepiece is variably transmissive to maintaincontrast between the real world ambient lighting and the virtual imagelighting. For example a photosensor detects ambient lighting. A biasvoltage is generated which applies a voltage across a photochromaticmaterial to change the transmissiveness of the eyepiece 20.

Eye Mapper

The eye mapper 40 is positioned between the light source 12 and thescanning subsystem 16. In an embodiment where the optics subsystem islocated between the light source 12 and the scanning subsystem 16, theeye mapper 40 is positioned between the optics subsystem 14 and thescanning subsystem 16. The eye mapper 40 includes a beamsplitter 42, aconvergent lens 43, and a photodetector 44. The photodetector 44generates an electronic signal which is input to the processor 13. Inone embodiment the processor 13 is part of a computer which generatesthe image data for the display 10. The beamsplitter 42 passes light 36which is incident in one direction and deflects light 48 which isincident in the opposite direction. Specifically, the beamsplitter 42passes light 36 received from the light source 12 and deflects light 48reflected back from the viewer's eye E through the scanning subsystem16.

To form an image on the viewer's retina light 36 emitted from the lightsource 12 passes through the optics subsystem 14, through thebeamsplitter 42, into the scanning subsystem 16 and on to the eyepiece20 and the viewer's eye E. Some of the photons of light are absorbed bythe eye's retina. A percentage of the photons, however, are reflectedback from the retina. The reflected light 48 travels back through theeyepiece 20 and is deflected by the scanning subsystem 16 back to thebeamsplitter 42. The beamsplitter 42 deflects the reflected light 48toward the photodetector 44. The photodetector 44 samples the reflectedlight content generating an electronic signal 50.

Mapping a Viewer's Retina

According to one method of this invention, the retinal display 10 witheye mapper 40 is used to map a viewer's eye. FIG. 3 shows a diagram ofan exemplary retina R of a viewer, as mapped according to an embodimentof this invention. The human retina includes a fovea 52 and severalblood vessels 54 which are poor reflectors of light. Other parts of theretina R are better reflectors of light. Of the photons reflected backfrom the retina R, there is relatively less reflection at the fovea 52and the blood vessels 54 than at other portions of the retina.

To generate an image on the viewer's retina R, the image is scanned in araster or other prescribed pattern. For example, a light beam ismodulated as the beam moves horizontally across an eye. Multiplehorizontal rows 56 are scanned onto the eye to complete the rasterpattern. The timing for modulating the light beam is synchronized sothat the row consists of multiple pixels 58 of light. Thus the rasterpattern includes multiple rows 56 and columns 60. When the light isforming a pixel at a given location on the retina R, such location alsomay reflect a portion of the impinging photons back into the display 10.Such photons form light 48 reflected back through the eyepiece 20 andscanning subsystem 16 to the beamsplitter 42. The photons are thendeflected to the photodetector 44. A given sample of reflected light 48comes from a given part of the retina and correlates such part of theretina to the relative position of the scanner within its raster patternat the time such reflected light is detected. Along the course of araster scan of the image onto the eye, there is a pattern of lightreflected back to the eye. While generating a map of the retina, thelight source 12 typically does not modulate the light. As a result, anychanges in light incident on the photodetector 44 is due to a change inreflectance at a portion of the retina. Alternatively, the lightstriking the retina may be modulated and synchronously detected forgreater noise immunity. In another alternative, modulated image lightmay be used to map the retina. Variations in intensity or content arefiltered out by conventional comparison techniques for common moderejection. A sample of the electronic signal generated by thephotodetector 44 is taken for each pixel scanned onto the eye. For eachpixel, the reflected light is registered as a high or a low logic state.One logic state corresponds to reflected light being above a thresholdintensity. The other logic state corresponds to the reflected lightbeing below the threshold intensity. The samples compiled for an eye area map of such eye's retina R. The resulting map is stored for use invarious applications. Using conventional image processing techniques,the pattern of logic states are analyzed to define the fovea 52 and oneor more blood vessels 54. Preferably, when compiling a map of a viewer'sretina, the viewer is instructed to look straight ahead at an unchangingimage. Alternatively, where the scanning subsystem is sufficiently fast,the mapping may occur during real time-meaning the eye mapper 40 can mapthe eye features simultaneously with virtual image generation.

Tracking a Viewer's Eye Position

One application of the eye mapper 40 is to track a viewer's eyeposition. According to one embodiment of this invention, the location ofthe viewer's fovea within a map at a given point in time is taken as thedirection in which the viewer is looking. For example, FIG. 3 shows thefovea 52 at the center of the retina R. This corresponds to the viewerlooking straight ahead. FIG. 4 shows a view of the same retina R withthe viewer looking in a different direction. In FIG. 4 the fovea 52 isto the left of center and upward of center. From the viewer'sperspective, the viewer is looking right of center and upward. Theamount the fovea has moved left of center and upward of centerdetermines the degree that the viewer is looking right of center andupward, respectively. Precise angles can be achieved for the viewingangle based upon the location of the fovea 52.

Rather than monitoring relative change in orientation of the fovea, inan alternative method the location of the fovea within the currentscanning pattern is identified. The processor uses the position of thefovea to identify a group of pixels that the viewer is focusing on. Theidentification of the group of pixels determines a viewing orientationwithin the current field of view. Alternatively, the viewing orientationcould be correlated to an external environment, such as the airspacearound aircraft. The correlated location or orientation in the externalenvironment may be used for image capture (e.g., photography), weaponstargeting, navigation, collision avoidance, human response monitoring,or a variety of other applications.

Method for Identifying Viewer

An application for using a stored map of a viewer's eye is to identifythe viewer. For example, only authorized viewer's having maps of theirretina previously stored on a computer system may be allowed access tothe computer system of to select information on the computer system orcomputer network. In a preliminary mode, a map of a user is obtained andstored. A set of access privileges then are identified and programmedinto the computer system for such user. When such user desires to accessthe computer system, the user's retina is scanned. Such scanning resultsin a second map of the viewer's retina R. Such second map is compared tothe previously stored map. If the two maps correlate within to athreshold percentage, then the user is identified as being the user forsuch stored map. Preferably, the user is instructed to look at the sameangle as when the initial map was obtained and stored. However, theprecise viewing angle may not be achievable by the viewer. However, bycomparing the relative location between the fovea 52 and various bloodvessels 54, the two maps are correlated. Thus, even for a differentviewing angle the pattern of blood vessels and the fovea will be thesame, just skewed. Depending on the degree of difference in the viewingangle, the skew may or may not be linear. The skew is nonlinear becausethe retina is not flat. As the retina moves the angle changes theapparent skewing. However, using conventional correlation techniques itcan be determined, for example, that the retina of FIGS. 3 and 4 are thesame. The viewer is just looking at a different direction for the twofigures.

Method for Pointing Within an Image

As described above, the position of the fovea 52 is used to identify theviewing angle. The position of the fovea 52 is tracked over time as theviewer moves their eye. At any given instant, such viewing angle defineswhere within the virtual image the viewer is looking. Specifically, theviewing angle correlates to a specific location on the virtual image.According to an embodiment of this invention, such specific location isused to define a pointer for the viewer. For example, in one embodimenta cross hair is overlaid onto the virtual image at the location wherethe viewer is looking. In another embodiment a cursor is overlaid. FIG.5 shows an exemplary virtual image 62 with an overlaid cross-hair 64.Such cross-hair is overlaid onto the virtual image within 1-2 frames ofthe image, (e.g., frames are updated at approximately 60 Hz; fasterrefresh rates also are known for displaying image data). Such 1-2 framelatency is a substantial improvement of prior eye tracking devices. Thelatency is low according to this invention, because the position of thereflected light returning from the eye is immediately correlated to theparticular pixel within the raster pattern. The overhead for identifyingand updating the fovea position and for altering the location of thecross hair in the output image is minimal and is done within a frameperiod (i.e., resulting in a 1-2 frame latency).

According to another aspect of this invention the viewer's eye not onlyfunctions as a pointing device (e.g., a mouse) but also functions as aclicking device (e.g., a mouse button). In one embodiment two blinkscorrespond to a click of a mouse. Alternatively one blink can be used ormore blinks can be used. Use of at least two blinks, however, is lesslikely to result in inadvertent clicking due to inadvertent blinking bya user. FIG. 6 shows an example where a viewer points to a menu line 66along the top of a virtual image 62. By blinking or double blinking at agiven menu within the menu line 66, the menu opens. FIG. 6 shows a menu70 pulled down. The viewer then can select an item within the menu 70.As shown, the viewer is looking at the third item in the menu 70.

FIG. 7 shows another application of the pointing and clicking functions.The viewer is looking at a target image 72 within the virtual image 62.By blinking or double blinking on such target image 72, text or graphicinformation relating to such target appears on the image 62. Suchinformation is applied at a prescribed location. In the illustratedexample, information of the target image 72 appears in the lower righthand corner of the image 62. Because the computer system generates thevirtual image and knows the content of the virtual image and knows wherethe viewer is looking when the viewer blinks, the computer can determineat what portion of the virtual image 62 the viewer is looking.Information about such portion, if any, then is overlaid onto the image62.

Although a preferred embodiment of the invention has been illustratedand described, various alternatives, modifications and equivalents maybe used. For example, although the embodiment described herein maps theuser's retina, the display may alternatively map other features of theeye, such as iris characteristics or capillary structures. Therefore,the foregoing description should not be taken as limiting the scope ofthe inventions which are defined by the appended claims.

What is claimed is:
 1. A method for determining viewing orientation ofthe viewer's eye with a virtual retinal display, the method comprisingthe steps of:generating visible light; receiving the generated visiblelight at an input of a lensing system, the lensing system defining anoptical path from the input toward an output, the lensing system outputadapted for transmitting light to and receiving light from a viewer'seye; receiving, at the lensing system, output light reflected from theviewer's eye; directing a portion of the light reflected from theviewer's eye toward an optical detector; generating an electrical signalcorresponding to the directed portion of light; and analyzing theelectrical signal over time to identify select characteristics of theviewer's eye, the select characteristics being indicative of the viewingorientation.
 2. The method of claim 1, in which the selectcharacteristics are retinal characteristics.
 3. The method of claim 1,in which the select characteristics are iris characteristics.
 4. Themethod of claim 1, in which the select characteristics are capillarystructures of the viewer's eye.
 5. The method of claim 1, wherein theselect characteristics correspond to a fovea of the viewer's eye.
 6. Themethod of claim 1, further comprising the step of:generating a pluralityof signals indicative of a map of the viewer's eye based upon a group ofsaid electrical signals produced over time.
 7. The method of claim 1,further comprising the step of:generating a virtual image output to theviewer's eye through the lensing system; and overlaying a display objectwithin the virtual image as a function of the viewing orientation. 8.The method of claim 1, further comprising the step ofdeflecting thegenerated light along a raster pattern; and concurrently deflecting thereflected light received from the viewer's eye.
 9. A method foridentifying a viewer's eye orientation with a virtual retinal display,the method comprising the steps of:receiving an image data signal at thedisplay to define image content of an image to be scanned upon aviewer's retina; generating light modulated as a function of the imagedata signal; deflecting the light along a raster pattern onto theviewer's eye with a light scanner; receiving returning light reflectedfrom the viewer's eye at the light scanner, deflecting the returninglight; directing at least a portion of the deflected light toward anoptical detector; generating a first signal at the optical detector inresponse to detection of the returning light; and identifying a viewer'seye orientation based upon relative location of a select data patternwithin the first signal.
 10. The method of claim 9, in which the selectdata pattern corresponds to retinal characteristics of the viewer's eye.11. The method of claim 9, in which the select data pattern correspondsto iris characteristics of the viewer's eye.
 12. The method of claim 9,in which the select data pattern corresponds to capillary structures ofthe viewer's eye.
 13. The method of claim 9, wherein the select datapattern corresponds to a fovea of the viewer's eye.
 14. The method ofclaim 9, further comprising the step of positioning a display objectwithin the virtual image as a function of the viewer's eye orientation.15. A method for generating a map of a viewer's retina with a virtualretinal display, the method comprising the steps of:generating light;receiving the generated light at an input of a lensing system, thelensing system defining a first optical path from the input toward anoutput, the lensing system output adapted for transmitting light to andreceiving light from a viewer's eye; receiving light reflected from theviewer's eye at a beamsplitter located in the optical path; redirectingwith the beamsplitter the reflected light along an alternative opticalpath; detecting the redirected light with an optical detector positionedin the alternative optical path, the optical detector responsive to theredirected light to produce an electrical signal corresponding to theredirected light; determining viewing orientation of the viewer's eyeusing the electrical signal; generating a virtual image output to theviewer's eye through the lensing system; and overlaying a virtualdisplay object within the virtual image responsive to the determined eyeorientation.
 16. A method for generating a map of a viewer's irischaracteristics with a virtual retinal display, the method comprisingthe steps of:receiving an image data signal at the display to defineimage content of an image to be scanned upon a viewer's retina;generating light modulated as a function of the image data signal;deflecting the light along a raster pattern with a light scanner;receiving returning light reflected from the viewer's eye at the lightscanner, deflecting the returning light toward a beamsplitter; directingsaid deflected returning light with the beamsplitter toward an opticaldetector; generating a first signal at the optical detector in responseto detection of the returning light; and correlating respective samplesof the first signal to corresponding timing positions within the rasterpattern, wherein the correlated samples define the map of the viewer'siris characteristics.
 17. The method of claim 16, further comprising thesteps of:storing the map as a first map; and comparing a second map tothe first map to determine whether the first map and second mapcorrespond to a same eye.
 18. The method of claim 17, further comprisingthe step of identifying a viewer's eye position over time based uponrelative location of a select data pattern within the first signal,wherein the select data pattern corresponds to a fovea of the viewer'seye.
 19. The method of claim 16, further comprising the step ofoverlaying a virtual display object within the virtual image as afunction of the viewer's eye position.
 20. A method for generating a mapof a viewer's eye capillary structures with a virtual retinal display,the method comprising the steps of:receiving an image data signal at thedisplay to define image content of an image to be scanned upon aviewer's retina; generating light modulated as a function of the imagedata signal; deflecting the light along a raster pattern with a lightscanner; receiving returning light reflected from the viewer's eye atthe light scanner, deflecting the returning light toward a beamsplitter;directing said deflected returning light with the beamsplitter toward anoptical detector; generating a first signal at the optical detector inresponse to detection of the returning light; and correlating respectivesamples of the first signal to corresponding timing positions within theraster pattern, wherein the correlated samples define the map of theviewer's eye capillary structures.
 21. The method of claim 20, furthercomprising the steps of:storing the map as a first map; and comparing asecond map to the first map to determine whether the first map andsecond map correspond to a same eye.
 22. The method of claim 20, furthercomprising the step of identifying a viewer's eye position over timebased upon relative location of a select data pattern within the firstsignal, wherein the select data pattern corresponds to a fovea of theviewer's eye.
 23. The method of claim 20, further comprising the step ofoverlaying a virtual display object within the virtual image as afunction of the viewer's eye position.
 24. A display apparatus,comprising:an image source for generating light; a lensing system havingan input aligned to the image source for receiving the generated light,the lensing system having an output adapted for transmitting light toand receiving light from a viewer's eye; an optical detector, whereinthe lensing system defines a first optical path from the input to theoutput and a second optical path from output to the optical detector,and wherein the optical detector is responsive to light along the secondoptical path to produce an electrical signal corresponding to said lightalong the second optical path; a memory device storing data representinga reference level; and a processor coupled to the detector and to thememory device, the processor being responsive to the electrical signaland the data to produce a signal indicative of a relationship betweenthe electrical signal and the reference level.
 25. The display apparatusof claim 24, in which over time the processor produces a first group ofindicative signals which are stored in the memory device and correspondto a map of the viewer's eye.
 26. The display apparatus of claim 25, inwhich the map is a first map, and wherein over time the processorproduces a second group of indicative signals which correspond to asecond map of the viewer's eye, the processor comparing the second mapto the first map to determine whether the first map and second mapcorrespond to a common eye.
 27. The display apparatus of claim 26, inwhich the processor comprises means for identifying a viewer's eyeorientation based upon relative location of a select data pattern withinthe electrical signal.
 28. The display apparatus of claim 27, in whichthe processor comprises means for overlaying a virtual display objectwithin the virtual image as a function of the viewer's eye orientation.29. The display apparatus of claim 24, further comprising a scanneralong the first and second optical paths, the scanner deflecting thegenerated light along a raster pattern, the scanner concurrentlydeflecting the light received from the viewer's eye.